how do you measure the mass of air inside a bell jar?

Answer 1

Argh...those other answers are way too complex...we don't need equations, save one: W = mg.

Now...
1. weigh the empty jar with air in it (W1)
2. seal the air-filled jar
3. pump out the air to form a vacuum inside
4. weigh the vacuum filled jar (W0)
5. note the difference in weight (W1 - W0) = W; the weight (not mass) of the air you pumped out
6. calculate the mass = (W1 - W0)/g = W/g; where W1 is the air filled jar weight in pounds, W0 is the vacuum filled jar weight in lb, and g = 32.2 ft/sec^2. The mass (m) unit is in slugs.

There will be some error because one cannot form a perfect vacuum. But the answer you get (m = W/g) will be close enough for most purposes.

Answer 2

You need to find the volume this Jar. Then you have to know the density of the gas in that time temparature .
Then put the formula

M=D*V [M=mass,,D=dansity,,V=volume..]

Your problem solved ..Have a nice day.......

Answer 3

measure the pressure volume and temperature then use the ideal gas law to calculate the number of moles of gas

PV=nRT

where p=pressure, v=volume, n=number of moles, R is the gas constant and T is the temperature

Then you could either lookup the composition of air or perform mass spectrometry to find the exact composition.

Then multiply the number of moles of each component by its molecular mass.